A. Field of the Invention
This invention relates to a variable speed ratio transmission that is used in the transmission of power between a motor, for example an engine or a person, and an output shaft. The speed of the output shaft varies automatically in response to load demand such that an infinite number of speeds between the minimum and maximum are available. The transmission of the present invention includes the use of a flexible belt for transmitting rotary motion between a driving shaft and a driven shaft.
This device is intended to be used on but not limited in application to any number of low horsepower devices such as bicycle, golf carts, machine tools, and preferrably wheelchairs. Also, any machine or vehicle that is required to deliver varying torques at varying speeds may be suitable for the application of the present invention.
B. Description of the Prior Art
One of the best known devices for accomplishing variable-speed transmission through the use of a belt is the Reeves variable speed transmission. Other efforts to achieve speed change include transmissions comprising pulleys that have peripheral belt or chain engaging surfaces that expand and contract radially. U.S. Pat. No. 672,962 discloses this type of prior art device.
U.S. Pat. Nos. 616,630 and 698,854, issued to J. C. Pratt, disclose transmissions having automatic variable speed change. Automatic varying speed ratio transmissions of the prior art that include expanding pulleys do not provide a very large change in speed ratio between the minimum and maximum values. The devices of the prior art are complex and require a large assembly of parts. Also, some of the larger, more efficient transmissions are inadequate for application in low horsepower devices.
One problem shared by all belt drive transmissions is the tendency for the belt to slip. The problem is more difficult to overcome when the transmission includes an expanding pulley. Lee, in U.S. Pat. No. 3,935,751, discloses the use of an idler pulley that is spring biased for tightening the belt. The addition of an idler pulley is not advantageous since there is an additional power transmission loss due to friction. Also, the added friction results in additional belt wear. Another method of solving the problem includes using two expanding pulleys that are spring biased in opposite rotational directions as taught by Pratt.